Today's respirators have no indicator when a breakthrough of harmful gases occurs in their cartridges. Instead the user has to rely on making conservative estimates from previously gathered data, which leads to disposing of cartridges that have a lot of remaining life and, sometimes, to non-detected breakthroughs of cartridges that expose the user to dangerous gases. We could use an End-of-Service-Life Indicator (ESLI) to forecast the breakthrough of harmful gas. An ESLI should provide reliable and accurate warning before 90% of the useful life of the cartridge (which is the regulatory requirement from NIOSH; the useful life is the time when harmful gases do not exceed the permissible exposure limits at the user).
One way of adding an ESLI is integrating the ESLI system into the cartridge (with absorbent downstream from the sensor); but this increases cartridge costs and complicates the communication with the sensor. Additionally, we would have to have as power supply either a disposable battery in the cartridge (costs!) or complicated wiring in the connector thread from the respirator housing. So far, the multiple attempts to integrate ESLI sensors into the cartridges, are believed to have been commercially unsuccessful.